The ethers file maps Ethernet addresses to host
names. Lines consist of an address and a host name, separated by any number of
blanks and/or tab characters. A ‘#’
indicates the beginning of a comment; characters up to the end of the line are
not interpreted by routines which search the file.

Ethernet addresses are expressed as six hexadecimal numbers separated by colons.
The functions described in
ethers(3) can read
and produce this format.

The ethers file has support for YP functionality,
which is enabled by specifying a ‘+’
alone on a line.